Carrier for mechanically-recorded records and method of making the same



A ril 12, 1938. c, J, DIPPEL 2,113,784

CARRIER FOR MECHANICALLY RECORDED RECORDS AND METHOD OF MAKING THE SAME Filed Jan. 8, 1937 Carrie Z is dDz'ppeZ Ptenteol Apr, l2, 1&8

CARRIER FOR MECCALLY-RECORDED lstgfigRDs AND DIETHOD OF MAKING THE Cornelia Johannes Dippel, Eindhoven, Netherlands, assignor to N. V. Philips Gloeilampenfabrieken, Eindhoven, Netherlands Application January 8, 1937, Serial No. 119,703 In Germany January 11, 1936 9 Claims. (01. 274 4e) My invention relates to carriers for mechanically-recorded vibration tracks, and more particularly to film carriers for mechanically-recorded and optically-reproducible sound tracks.

produced by the above method, or by other mechanical recording methods, must meet several requirements. For example, the surface of the vibration track should have a polished or at least an unfrosted appearance. If the reproduction is effected with transmitted light it is important that the transparent material of the record be homogeneous and not contain any irregularly- -divided quantities of substances having different optical properties.

For recording of the above type it has been proposed to use a carrier having a separate re-' cording or cutting layer of gelatin. However, the commercial gelatin used for this purpose has several disadvantages, especially in mechanical recording of. the type described in the abovementionedpatent. For example, when cutting a vibration track, especially with the V-shaped cutting tool of the above mentioned type, the cutting resistance of such a commercial gelatin is so high that it'necessitates the use of a high controlling energy in the recording device, and

may also damage the cutting edge of the recording tool-L1 Furthermore, the usual commercial types of'gelatin are so elastic that they are not cleanly cut by the recording tool, but are torn in an irregular manner. Such tearing, of course is detrimental to the optical reproduction, especially with respect to the high frequencies, as

pose gelatin to a lower molecular colloid, and that in the manufacture of gelatin various grades of gelatins are obtained by separating them from various fractions obtained during the manufacture. In such cases however, the fractions which 3 are decomposed to the highest extent are the last obtained, and these fractions contain such an accumulation of impurities that they constitute the poorest grades and can neither be considered as a material for use for carriers of vibration tracks, nor can they be made suitable for this purpose; as the removal of the impurities is impractical from a commercial and technical standpoint. However, in the present invention, I

use as the starting material a gelatin obtained in the preparation of gelatin as a much purer fraction and in a state of decomposition which has proceeded to a smaller degree, i. e., those fractions which possess about the state of decomposition of commercial photographic gelatin of so-called medium quality. I

In order that my invention may be clearly understood and readily carried into efiect, I shall describe same in more detail with reference to the accompanying drawing in which the single 55 As my invention is particularly advantageous it causes irregularities in the boundary lines and 5 with the method of mechanical recording set surface of the vibration track. Furthermore, the forth in U. S. Patent No. 1,919,116 to James A. impurities, which are always present to a more Miller, I shall describe same in this connection. or less degree in all gelatins, are rather securely However, my invention extends to other types of held in the relatively hard commercial gelatins mechanically recording vibration tracks which and damage the cutting edge of the recording are optically-reproducible by either transmitted tool during the recording. In addition, the sur- O efl c d htface of such gelatins may become frosted in time.

In recording by the method of the above-mew which impairs the optical reproduction. tioned patent, a cutting tool having a V-shaped The object of my invention is to overcome the cutting edge with an apical angle of about 174 above difficulties and to provide a carrier in which is oscillated, in accordance with the vibrations a vibration track capable of being optically reto be recorded, substantially perpendicularly to produced in an accurate manner can 'be methe surface of a moving carrier pr g a chanically recorded without damage to the retransparent cutting or recording layer and an cording tool. opaque covering layer, and produces therein a In accordance with the present invention, I vibration track having width variations which use as the material for cutting or recording layer are a pr p rt na enlargement'of the deD a gelatin obtained by decomposing a commercial ations. Such a track is pa t u y Suited r gelatin into a lower molecular colloid. More par-, p a production, as the Small a p ticularly I start with a commercial gelatin which w 's al y orr p nd t h hi h eis not too much decomposed, for instance, photo- 5 .quencies, are accurately recorded, and it is graphic gelatin of the so-called medium quality, :p 11 retain s p p y of the record as and decompose this gelatin at the utmost to such much as possible d ri g i further illefillilnellt,- an extent that it still gelatinizes in a 10% solufor instance during the reproduction. I w t ab t 15 c,

Toinsure p p Optical p o t a record I am aware that it is known Der se to decomflowers on a windowpane.

figure is a perspective view of a carrier and shows a cutting tool cutting atrack therein.

The carrier shown in the drawing comprises a base layer 1 of transparent material, for instance Celluloid, a recording or cutting layer 2 of gelatin, and a thin covering layer 3 of an opaque material. A cutting tool 4 having a V-shaped cutting edge'with an apical angle a, is vibrated in the direction of the double-headed arrow in accordance with the vibrations to be recorded to produce in the carrier an opticallyreproducible vibration track 5, the carrier being moved at a constant speed in the direction of arrow 6. In practice the angle a is about 174, however it is shown smaller in the drawing for clarity.

In accordance with the invention I use as the material of the cutting layer 2 a gelatin obtained by decomposing commercial gelatin into a lower molecular colloid, i. e. at the utmost to such an extent that the material of the layer 2 will still gelatinize in a 10% solution at about 15 C. In the manufacture of such material I use as a starting material a commercial gelatin which has not been decomposed to too great a degree, for example a gelatin of the order of photographic gelatin of so-called medium quality.

I further decompose such a starting gelatin, which is rather pure, for example by a thermal process or by the action for example of lyes to obtain gelatin of the desired quality. However, as such methods of decomposition at present entail various manufacturing difficulties, I prefer to carry out the decomposition by a chemical agent for example by the action of an acid such as HCl.

Although decomposition with an acid can be carried out commercially in a satisfactory manner, and results in a gelatin which unconditionally meets the requirements of the mechanical recording, I have found that when using acids, additional measures must be employed to obtain a cutting layer which is as perfect as possible.

' In many instances, the cutting layers according to the invention do not have the desired stability, i. e. after a shorter or longer time depending upon atmospheric conditions, the initially perfectly smooth and clear surface of the sound track becomes rough or frosted, i. e. coarse crystals cover the surface of the layer like "frost This phenomenon is probably due to a process of crystallization, and

such a frosted surface is evidently inadmissible as it causes a strong ground noise du'ring the reproduction and thus may seriously injure the quality of the record. It is possible to ascertain in a simple manner whether a certain grade of gelatin will exhibit this phenomenon by placing -a portion of the film for about 50 hours in an atmosphere substantially saturated with water vapor to accelerate the process.

I have found that in general this phenomenon of crystallization is particularly due to calcium salts, for example calcium sulphate, calcium phosphate, etc.

As is known, crude gelatin contains a considerable quantity of calcium compounds originating from the material from which the gelatin is made, i. e., hides, bones, hoofs, etc.; the calcium generally being present in the form of diflicultly soluble salts, such as phosphates. For ordinary purposes the calcium is removed'from the gelatin by various methods of dialysis which are known per se. However, I have found that gelatin which has been thus freed from calcium salts.

salts-more particularly gelatin decomposed by acidsstill contains such a quantity of these salts that the mechanical recording is deleteriously affected.

Although other explanations may be later found forthe above action, I believe that the treatment with an acid causes the formation of a fairly large number of free calcium ions in the gelatin, and that these ions are isolated together with the free phosphate or sulphate ions likewise present in the gelatin, in the form of coarse andinsoluble calcium phosphate or calcium sulphate crystals which produce the frosted surface of the-layer. I have also found that with types of gelatin which are free from calcium to a high degree, for instance certain hide gelatins, there is no crystallization, and that ordinary gelatins may be treated in such a manner that harmful crystallization is presented. However it is impractical to obtain the desired. purity by simply continuing the dialysis process, as with ordinary gelatin it would be necessary to continue the process for an impractical length of time. This harmful crystallization can, of course, be avoided by using as a starting material a type of gelatin which contains no, or only a slight amount of, harmful salts, particularly calcium However, such gelatins are so expensive that it is preferable to start with a cheaper type.

In accordance with another feature of my invention, I prevent the formation of harmful crystals on a cutting layer formed by decomposing a commercial gelatin with an acid, by neutralizing the added acid to a sufficient extent and then treating the gelatin to a usual dialysis process. With such a method it appears that the free ions present are removed to such a degree that harmful crystallization cannot occur, and that no new free calcium ions will form.

Furthermore, this process has the additional advantage that in general any impurities which might still remain in the gelatin can be readily removed. More particularly, often the gelatin has been decomposed'with the aid'of acid for a sufficient time, it is only necessary to remove at least the greater part of the calcium ions by washing, i. e. by dialysis with water.

, Although during neutralization some salts, which-for the most part are insoluble, are produced, this is not a drawback as they occur in only small quantities and are in the form of very small crystals. Provided care is taken to prevent the further addition of an acid, recrystallization of these fine crystals into crystals of harmful size will not occur.

In many cases it is of advantage to add to the gelatin according to the invention a certain quantity of the oil known under the trade name Tiirkondl. The use of such an oil has been described in my U. S. Patent 2,019,215 dated October 29, 1935.

A cutting layer of a gelatin according to the invention has a low resistance to the recording tool, and has a low elasticity thereby eliminating damage to the track due to a tearing thereof by the tool. Furthermore the layer is relatively soft so that the impurities, which are always present to a more or less degree in any type of gelatin, are not so firmly held and are pushed aside by the recording tool without damage to the cutting edge.

While I have described my invention in connection with specific examples and applications, I do not wish to be limited thereto, but desire the appended claims to be construed as broadly as permissible in view of the prior art.

What I claim is:

1. A carrier for mechanically-recorded vibration tracks comprising a recording layer consisting substantially of decomposed gelatin in a lower molecular colloid than commercial gelatin, a 10% solution of the mass of said layer still just gelatinizing at about C.

2. A carrier for mechanically-recorded vibration tracks comprising a recording layer consisting substantially of decomposed gelatin in a lower molecular colloid than commercial photographic gelatin of so-called medium quality, a 10% still just gelatinizing at about 15 C.

3. A carrier -for mechanically-recorded and optically-reproducible vibration tracks comprising a base layer of transparent material, a recording layer, and a covering layer of opaque material, said recording layer consisting substantially of decomposed gelatin in a lower molecular colloid than commercial photographic gelatin of so-called medium quality, a 10% solution of the mass of said recording layer still just gelatinizing at about 15 C. I

4. In the manufacture of carrier for mechania cally-recorded vibration track, the method of making a recording layer comprising the steps, decomposing a commercial gelatin which is not too much decomposed into a lower molecular colloid and at the utmost to a degree at which a 10% solution of the mass of the layer still gelatinizes at about 15 C., and forming the recording layer from the decomposed gelatin.

5. In the manufacture of carriers for mechanically-recorded vibration tracks, the method of making a recording layer comprising the steps, decomposing a commercial gelatin of the order of commercial photographic gelatin of so-called medium quality into a lower molecular colloid and to a degree at which a 10% solution of the gelatin will still gelatinize at about 15 0., and

solution of the mass of said recording layer forming the recording layer from the decomposed gelatin. I

6. In the manufacture of carriers for mechanically-recorded vibration tracks, the method of making a recording layer comprising the steps, chemically decomposing a commercial gelatin which is not too much decomposed into a lower molecular colloid and at the utmost to a degree at'which at 10% solution of same still gelatinizes at about 15 C. and forming the recording layer from the decomposed gelatin.

'7. In the manufacture of carriers for mechanically-recorded vibration tracks the method of making a recording layer comprising the steps, treating commercial gelatin of the order of photographic gelatin of so-called medium quality with an acid to decompose same into a lower molecular colloid and to a degree at which a 10%- solution of the gelatin will still gelatinize at about 15 C., and forming the recording layer from the decomposed gelatin.

8. In the manufacture of carriers for mechanically-recorded vibration tracks, the-method of making a recording layer comprising the stem, treating with an acid a commercial gelatin substantially free from harmful calcium salts to depompose the gelatin into a lower molecular colloid and to a degree at which a 10% solution of same still gelatinizes at about 15 C., and forming from the decomposed gelatin a recording layer free from harmful crystallization.

9. In the manufacture of carriers for mechanically-recorded vibration tracks, the method of making a recording layer comprising the steps, treating commercial gelatin of the type of photographic gelatin of so-called medium quality with an acid to decompose same into a lower molecular colloid and to a degree at which a 10% solution will still gelatinize at about 15 0., neutralizing the added acid and washing the gelatinby a usual dialysis process to prevent harmful crystallization of the layer, and forming the layer from the so-obtainedgelatin.

CORNELIS JOHANNES DIPPEL. 

